Plane Lace Bug: A Delicate Micro Menace Concealed in the City

Anyone walking down a central London street will no doubt have viewed the towering presence of the great London plane trees (scientific name: Platanus × hispanica) which have been a constant presence in London and other UK cities since the 18^th century. The London plane trees seen today are a hybrid of the Oriental plane (Platanus orientalis) and the American sycamore (Platanus occidentalis) and they are celebrated for being very hardy, pollution tolerant, long lived and majestic trees. It is said that some of the first planes of this hybrid were planted at the Palace of Versailles in the late 17^th century, but it is also claimed that the first hybrid plane was found in London in the same period. Whichever historical version is correct, by the mid-18^th century, this plane hybrid had become a popular municipal street tree in London, where today, centuries old trees keep the pollutants down and help shade the streets and people of the city.

On the 25^th of July 2024, a public observation was made on iNaturalist of an interesting tiny bug found on someone’s bag in central London. A scientist from Defra spotted the report and gathered more information from the informer, believing it to be a specimen of the plane lace bug (Corythucha ciliata) due to its lace-like appearance and the location of the find in central London, where London plane trees abound. Response managers were deployed from Forest Research & the Animal and Plant Health Agency to survey London planes on the streets and parks around the initial location of the find, and soon it was confirmed that lace bugs were in the area. A microscopic examination of the bugs by Fera Science Ltd. and Forest Research verified that the species was the plane lace bug (PLB).

This is not the first occurrence of PLB in the UK, as in 2006 a small and localised population was discovered at a plant nursey in Bedfordshire. However, trees were treated with pesticide and surveillance of the population over the following years found no evidence of the pest persisting in the area. Native to North America, this bug has spread across the world, and it is now found in Europe and as far as China and Australia. This pest can disperse through flight and is known to hitch-hike, moving around with the assistance of human movements, on clothing and vehicles. Trees which encounter high populations of PLB year after year can become weakened and susceptible to fungal attack, as well as other pathogens and insects. On otherwise healthy trees, thankfully, the effects of this pest are largely aesthetic.     

Following the finding in summer 2024, the Forestry Commission implemented an extensive surveillance programme for the plane trees across London. This survey work concentrated on areas of high footfall and transport hubs, given that the bugs can be easily transported by people, traffic, and the wind.   

By the middle of September 2024, Defra had confirmed to the UK public that PLB had been found on plane trees in central London. It stressed that, although PLB is not a regulated pest, it would however continue to monitor its presence. Plant Health Officers and contractors from the Forestry Commission, together with citizen scientists from Observatree, continued the surveillance work in London into the Autumn, with their data collated by Forest Research.

Those conducting the work were on the look-out for evidence of the tiny 4mm long adult lace bugs and their smaller black nymphs. Premature leaf-drop and the presence of chlorotic (pale/bronzing) leaves in the summer months, together with tiny dark specks of frass (droppings) on the underside of the leaves, can be signs of PLB presence. Chlorosis occurs as the bugs suck out and feed on the contents of the leaf cells which causes a colour change and eventual leaf death. Close-up visual examination of the leaves is enough to confirm the presence of a lace bug, and confirmation of the species identification can be made from high quality images.  

Plane trees across London and beyond were surveyed for the presence of PLB by professionals and volunteers, with members of Observatree keeping up the mantle until October when autumn fully took hold. A record number of PLB survey submissions to Forest Research’s pest and disease reporting line TreeAlert were made, with none  of these submissions between West Yorkshire and South London resulting in finding PLB in a new location. Observatree volunteers significantly increased their London plane TreeAlert reporting activity in 2024 compared with 2023, as a direct result of their call to help in the surveillance of this micro menace, with over 130 reports made through the platform since September 2024. The role of the Observatree volunteer citizen scientists in the surveillance of PLB will continue throughout 2025, as they will once again remain vigilant for signs of the plane lace bug amongst our wonderful London planes.  

So, next time you are walking below the leafy plane trees of the UK, or riding the upper deck of a bus where their leaves are often at eye level, take a look to see if you can spot the minute, yet specific, signs of PLB and submit a report through TreeAlert.